This invention relates to an improved analytical instrument. The invention relates more particularly to an analytical instrument utilizing nondispersive photometric techniques.
Various analytical apparatus are known which are adapted for the examination of a sample substance and which provide a qualitative indication of sample components, a quantitative indication, or at times both qualitative and quantitative information. Present day apparatus of this type provide a sequential presentation in time of the information of interest for the analytical chemist. For example, the analysis of a sample with a chromatographic instrument will produce a chromatogram having a sequence of peaks, the heights or areas of which can be related to the quantities of sample constituents for a known sample volume. While certain substances have recognizable peak retention times which permit a trained observer to some extent to also identify substances, the chromatograph is generally considered to be a quantitative instrument which is relatively unsatisfactory for qualitative examination of a sample constituent. In a spectrophotometric type of analytical instrument, a sample under investigation is examined by scanning with radiant energy of different frequencies to determine the wavelengths of radiant energy absorption, emission, fluorescence, or reflectance by sample components. A spectrogram is generated indicating the wavelengths at which peaks corresponding to absorption, emission, fluorescence or reflectance occur. The spectrogram is utilized principally to provide peak information from which sample components or their structure can be identified. While the spectrophotometer is primarily a qualitative instrument, it may be used at times for quantitative determinations by a trained analytical chemist. In this regard it provides a relatively accurate determination of the ratio of components of a sample when not too many sample components are present at the same time.
Present day chromatographs and spectrophotometers include means for providing a visual display of a sample analysis through the use of various readout devices. The chart recorder is a readout device frequently used with chromatographs and spectrophotometers. In addition some instruments also include means for calculating and providing numerical readouts of peak areas, peak heights, etc. as for chromatograms obtained with chromatographs, and, spectrograms with spectrophotometers.
It is desirable to provide an analytical instrument having means for simultaneously displaying informational peaks of a substance being analyzed. Analysis would be further enhanced if the sample substance is initially separated into components by a chromatograph and each of the components is photometrically analyzed. For example, the simultaneous presentation of photometric peaks would be advantageous in examining the effluent components from a gas or liquid chromatograph or for monitoring the flow-through of a fluid material in a flow process. Photometric analysis at infra-red (I.R.) frequencies is particularly useful since absorption frequencies exist which relate to functional groups in molecules and an observer can immediately determine from an absorption characteristic at a selected wavelength whether a component belongs to a particular class of molecules.
Analytical techniques are known wherein ultraviolet (U.V.) and fluorescence spectrophotometry and photometry at a preselected wavelength is utilized as a detection means with liquid chromatography. However, photometric techniques at the I.R. frequencies have not been utilized with liquid chromatography since most carrier liquids exhibit a relatively strong I.R. absorption characteristic which severely limits the analytical chemist in his selection of carrier liquids. While in the field of gas chromatography this carrier fluid limitation does not occur, nonetheless the relatively small sample volumes involved introduce a requirement for increased photometric sensitivity. A flow through detector cell for use with gas chromatography should have a volume of 20 microliters (.mu.1) or less. In certain forms of gas chromatographic instruments such as those utilizing open tubular capillary columns, the volume should be even less. The use of I.R. photometry for qualitative detection of separated sample components is desirable in view of its capability for indicating molecular classes. However, the sensitivity and speed of an I.R. spectrophotometer is inadequate for examination of these relatively small separated samples. Special I.R. spectrophotometers which provide substantially higher sensitivities and speed are costly necessitating elaborate design, while the desired simultaneous display, referred to above, require relatively elaborate quantometers or rapid scanning photometers, each of which is also relatively costly.
Accordingly, it is an object of this invention to provide an improved form of analytical instrument.
Another object of the invention is to provide an analytical instrument having chromatographic separation means and nondispersive, multiwavelength photometric sample component identification means.
Another object of the invention is to provide an improved form of analytical instrument having a gas chromatographic separation means and a nondispersive, multiwavelength, I.R. photometric means of sample component identification.
Another object of the invention is to provide an analytical instrument of the type described of relatively reduced complexity and cost.
Another object of the invention is to provide a nondispersive photometer having multiwavlength means for simultaneously displaying radiant quantitative data at different wavelengths.
Another object of the invention is to provide a nondispersive, multiwavelength photometer of the type described of relatively reduced complexity and cost.